Acupuncture charts printed by Imperial decree in 1906 from old blocks. Anterior view, showing the jingluo (meridians and collaterals) of the human body. Acupuncture is a form of alternative medicine in which thin needles are inserted into the body. It is a key component of traditional Chinese medicine (TCM). TCM theory and practice are not based upon scientific knowledge, and acupuncture is a pseudoscience. There are a diverse range of acupuncture theories based on different philosophies, and techniques vary depending on the country. Scientific investigation has not found any histological or physiological evidence for traditional Chinese concepts such as qi, meridians, and acupuncture points, and many modern practitioners no longer support the existence of life force energy (qi) flowing through meridians, which was a major part of early belief systems. Acupuncture is believed to have originated around 100 BC in China, around the time The Yellow Emperor's Classic of Internal Medicine (Huangdi Neijing) was published, though some experts suggest it could have been practiced earlier.